How to choose the medium for dispersion of materials during the UV-vis measurement?
If you are dealing with thin films, you can take transmission as a function of wavelength till you get interference fringes. Then you use Swanapoule method to calculate absorption coefficient as a function of energy., From this, you can get band gap using Tauc plot. The advantage of this method is that you can get real and imaginary part of refractive index as a function of wavelength and also film thickness. If you do not get interference fringes, then you have to measure reflection also as a function of wavelength to know the absorption and then to calculate absorption coefficient as a function of energy and then finally you can calculate band gap from Tauc plot. You can also calculate band gap from reflection data only if you are not getting transmission in case of bulk samples.
If you are dealing with thin films, you can take transmission as a function of wavelength till you get interference fringes. Then you use Swanapoule method to calculate absorption coefficient as a function of energy., From this, you can get band gap using Tauc plot. The advantage of this method is that you can get real and imaginary part of refractive index as a function of wavelength and also film thickness. If you do not get interference fringes, then you have to measure reflection also as a function of wavelength to know the absorption and then to calculate absorption coefficient as a function of energy and then finally you can calculate band gap from Tauc plot. You can also calculate band gap from reflection data only if you are not getting transmission in case of bulk samples.
Use UV-VIS DRS accessory if your materials is in powder form. and measure the % Reflectance, plot the differential curve of the spectra and find the band edge, then use equation BG =1240/lambda (band edge). you will get bandgap. you can refer my group work.
The above two answers are satisfactory. I have tried for both the methods. But the method suggested by Prof. Tayade is suitable very well implemented. That method is also called as Planks Einstein relation. Band gap energy (Eg )=(h*c)/λ, where λ is cutoff wavelength can be obtained from Uv absorbance spectra.
Here you can find good explanation and band gap calculator,
http://www.instanano.com/characterization/theoretical/uv-vis-spectroscopy-band-gap-calculation/
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